简介
new 实现学习笔记。
new 实现
function fakeNew(object) {
// == 1. 创建对象，同时设置该对象的 __proto__ 属性
let obj = Object.create(object.prototype);
// == 等价于
// == let obj = {};
// == obj.__proto__ = object.prototype;
// == 2、执行构造函数中的代码（为这个对象添加属性和方法）
let k = object.call(obj);
// == 3、返回对象
if (typeof k === 'object') {
return k;
}
return obj;
}
let M = function(name) {
this.name = name;
}
let obj = fakeNew(M);
console.log(obj instanceof M);
instanceof 实现
function fake_instance_of(left, right) {
let leftProto = left.__proto__;
let rightProto = right.prototype;
while (leftProto) {
if (leftProto === rightProto) return true;
leftProto = leftProto.__proto__;
}
return false;
}
Object.create 与 new 的区别
const a = { x: 1 };
const b = new Object(a);
console.log(b.__proto__ === Object.prototype);
const a = { x: 1 };
const c = Object.create(a);
console.log(c.__proto__ === a);